The present invention relates to a rubber composition containing a low air permeable rubber having a vulcanized functional group (hereinafter referred to also as xe2x80x9cfunctional group-vulcanizable rubberxe2x80x9d) and a rubber having a vulcanizable carbon-carbon double bond (hereinafter referred to also as xe2x80x9cdouble bond-vulcanizable rubberxe2x80x9d). Further in detail, the present invention relates to a rubber composition which is superior in adhesion properties to other diene rubber compositions when subjected to vulcanization and can provide a rubber molded article not inferior in low air permeability.
Hitherto, in order to gain performances which cannot be obtained by a rubber composition using only one rubber as a rubber component and also to achieve improvement in processability of the resulting rubber composition and cut costs of raw materials, a blend of two or more rubbers is employed.
Also, in the field of tires, particularly for an innerliner, a case or the like, since low air permeability and adhesion properties with respect to other diene rubber compositions when using vulcanization are necessary, there is employed a rubber composition of two or more rubbers, one of which is a rubber being able to provide low air permeability.
For improving low air permeability, when a proportion of a low air permeable rubber in the rubber composition comprising the low air permeable rubber and other rubbers is increased, for example, to not less than 50% by weight of the rubber component, however, there is a problem in that adhesion properties affected by vulcanization between the obtained rubber composition and other diene rubber compositions becomes considerably lowered.
On the other hand, with respect to a rubber composition comprising two or more rubbers, i.e. a functional group-vulcanizable rubber and a double bond-vulcanizable rubber, JP-A-121766/1996 discloses a rubber composition containing a selectively vulcanized functional group-vulcanizable rubber by carrying out a two-step kneading process. By vulcanizing the obtained rubber composition after molding, the double bond-vulcanizable rubber is also vulcanized and a rubber molded article which does not contain any rubber in a non-vulcanized state can be obtained.
Then, considering the above-mentioned facts, the inventors employ a specified combination of a low air permeable rubber having a vulcanizable functional group and a double bond-vulcanizable rubber at a specified mixing ratio using the above-mentioned two-step kneading method and, thereby, reach a method to obtain a rubber composition which can provide a rubber molded article superior in adhesion properties with respect to other diene rubber compositions by vulcanization and not in low air permeability.
An object of the present invention is to obtain a rubber composition which can provide a rubber molded article superior in adhesion properties with respect to other diene rubber compositions by vulcanization and not inferior with respect to low air permeability.